1. Field of the Invention
The present invention relates to a dry etching method, and more particularly to a method of selectively etching a semiconductor material through a photochemical reaction.
2. Description of the Prior Art
Heretofore, the reactive ion etching process has widely been used as a dry etching process for etching substrates in the fabrication of LSI circuits or the like. As the size of circuit functions per chip is reduced, the reactive ion etching process tends to cause more damage to substrates due to plasma reaction. Another problem of the reactive ion etching process is that since the configuration of the etched groove does not exhibit crystal anisotropy, the etched grooves cannot be used for anisotropic epitaxy.
Japanese laid-open patent publication No. 60-165725 (Japanese patent application No. 59-20995) discloses a photoetching process which applies a laser beam or ultraviolet radiation. According to the disclosed photoetching process which is one form of dry etching process, no damage is caused to substrates by plasma reaction and the etched surfaces of the grooves are available for anisotropic epitaxy.
According to the photoetching process, a material to be etched is housed in a vacuum chamber, and while an etching gas such as a reactive gas or the like is being introduced into the vacuum chamber, light that dissociates the etching gas is selectively applied to the region of the material which is to be etched. The depth to which the material is to be etched is basically determined by adjusting the amount of the etching gas to be introduced, the time during which the etching gas is to be introduced, and the time during which energy particles, i.e., light, are applied to the crystal surface of the material that is exposed to the etching gas, thereby controlling the time of a photochemical reaction.
As more and more circuit elements per chip are required in LSI circuits, pattern dimensions need to be smaller, and the etching depth also needs to be controlled with greater accuracy. For example, the fabrication of static induction field-effect transistors (SIT) of GaAs requires the etching depth to be controlled with an accuracy on the order of at least 10 .ANG. in order to etch an epitaxial layer that has been grown in terms of molecular layers.
However, such a high accuracy for the control of the etching depth cannot be achieved through the adjustment of the photochemical reaction time in the above photoetching process. In the actual fabrication of semiconductor devices, it has been necessary to control the etching depth as it is measured with an expensive etching monitor during the etching process, or to measure the etching depth with the etching monitor after the etching process and to additionally effect the etching process if the etching depth is not sufficient. Consequently, the conventional process of controlling the etching depth has been highly difficult to carry out and the reproducibility of the controlling process has been poor.